Copyright B. Bo Sramek

A new generation of TEB technology, discussed below, is an accepted, main stream
technology for noninvasive, continuous measurement of global blood flow (Cardiac
Index, CI - the global blood flow per minute, and Stroke Index, SI - the global blood
flow per beat),respiration and a host of cardiodynamic parameters.

The TEB is utilized in the TEBCO Module.TEBCO(Thoracic Electrical Bioimpedance
Cardiac Output) measures cardiac index (CI) and 9 other cardiodynamic
parameters (stroke index, heart rate, respiratory rate, ventricular ejection time,
pre-ejection period, ejection phase contractility index, inotropic state index, estimate
of ejection fraction, end-diastolic index,...) noninvasively with the same clinical
accuracy as the invasive thermodilution catheter,
however, without its cost, risk, need for sterile environment
and a skilled clinician. TEBCO's TEB measurement current is 300-to-400-times
lower than the measurement current of any competitive TEB/ICG product.

TEBCO OEM Module packaged in a stand-alone enclosure with its own
power source is an external TEB module EXT-TEBCO,
which is the blood flow measurement component of the HOTMAN System.

HOTMAN
System represents the advanced trend in changing the cardiovascular medicine from
monitoring patients (i.e., the reactive approach,
responding to a cardiovascular disaster already taking place) to hemodynamic management
of patients (i.e., the proactive approach, continually
providing the physician with information what therapy to implement in order to maintain
the normohemodynamic state). HOTMAN
Systems offers much better economics than a competitive
ICG monitor, when used in a physician's office or in hospital.

Thoracic
Electrical Bioimpedance (TEB), with a symbol Z [],
is an electrical resistance of the thorax to a high-frequency, very-low magnitude
TEB measurement current. TEB utilizes a patient's thorax as an impedance transducer.
The patient is connected to TEBCO via
a patient cable attached to eight solid-gel, disposable electrodes (see Fig.1 below).
The TEB measurement current is passed through the thorax in a direction parallel
with the spine between a pair of electrodes placed on upper neck and a pair of electrodes
placed on upper abdomen. On its way through the thorax, the TEB measurement current
seeks the shortest and the most conductive pathway. As a result, the majority of
the TEB measurement current flows through the thoracic aorta and vena cava superior
and inferior - their black outlines are shown in Fig.1 below. The TEB measurement
current produces a high-frequency voltage across the impedance of the thorax, directly
proportional to TEB. This induced high-frequency voltage is sensed by two other pairs
of electrodes placed inside the current path, i.e., at the beginning of the thorax
(the line of the root of the neck) and the end of the thorax (the level of diaphragm
- the xiphoid process level). These four sensing electrodes also detect four different
vectors of the ECG signal. The Heart Rate, HR, is derived from the
R-R intervals of the ECG signal. Due to anatomical shape of the thorax, a preferential
placement for all eight electrodes is along the frontal plane - the thoracic
widest dimension.

Fig.1: Location of the 8 electrodes along the TEB transducer - a patient's thorax.
The top and bottom pair is a source and sink of the TEB measurement current, the
inner pairs, located at the root of the neck (the beginning of the transducer) and
the diaphragm level, i.e., the xiphoid process level (the end of the transducer),
are used for sensing both the TEB signal and 4 different vectors of the ECG signal.

The TEB level (the Base Impedance, )[]
is indirectly proportional to total content of thoracic fluids, however,
it cannot identify individual conductance contributions of the intravascular, intra-alveolar
and interstitial compartements. Instead of ,
TEBCO, therefore, measures and displays its inverted value, i.e., the Thoracic
Fluid Conductivity, TFC [1/],
which is then directly proportional to the total thoracic fluids content.

The
TEB variations and changes (Z)
are produced by:

slow changes of fluid levels in all thoracic compartments - a result of
postural changes or, for instance, pulmonary edema,

volumetric (plethysmographic) and velocity (alignment of planes
of erythrocytes as a function of blood velocity) changes of aortic blood produced
by the heart's pumping (cardiodynamic) activity.

Fig.2: This picture documents the timing relationship between ECG, Z
and dZ/dt signals: Myocardial contraction starts at the Q-time of the ECG QRS complex.
The Pre-Ejection Period (PEP) [isovolumic contraction] is defined as the elapsed
time between the Q-time of the QRS complex and the opening of aortic valve. The ejection
phase, outlined by the Ventricular Ejection Time (VET), starts by opening of aortic
valve and ends by its closure (S2-time). During the initial portion of ejection phase
the aorta distends and the thorax, therefore, becomes more conductive; at the same
time the velocity of blood increases, more erythrocytes are aligned so their planes
are parallel with the main axis of aorta and, therefore, the blood becomes more conductive.

Fig.3: These are two
simultaneous recordings of ECG and dZ/dt as displayed on all screens of HOTMAN
System. To enable operator to confirm visually a detection of key points of the
dZ/dt signal and acceptance of that specific heart beat for calculation of SI
and other cardiodynamic parameters, the system adds to the dZ/dt signal an
upward 2-pixle line where it detected the aortic peak flow [(dZ/dt)max], and
adds a downward 2-pixle line where it detected the closure of the aortic valve
(the S2 time in Fig.2).

The rate of cardiovascular TEB changes over time (dZ/dt) [i.e., the first
derivative of Z]
is an image of the aortic blood flow. Its maximum value, [(dZ/dt)max],
is proportional to the aortic blood peak flow(please note the difference
between TEB measured peak blood flow and peak velocity measured by
Doppler technologies). The aortic blood peak flow is a mirror image of ejection
phase myocardial contractility. This parameter's value is influenced both by
the Frank-Starling mechanism (change in intravascular volume) and, pharmacologically,
by inotropes. TEBCO processes this parameter normalized by TFC
and displays it as the Ejection Phase Contractility Index, EPCI:

The maximum rate of the second derivative of Z [(dZ/dt)max],
is, therefore, an image of the maximum acceleration of aortic blood flow -
a true measure of inotropic state, essentially independent of preload and afterload
(a detailed discussion and physiologic explanation of these phenomena can be found
in the Chapter 7, Hemodynamics of the cardiovascular system, in the textbook Biomechanics
of the Cardiovascular Systemand in the textbook Systemic
Hemodynamics and Hemodynamic Management). TEBCO® measures the level of inotropic state through another normalized parameter - the Inotropic State Index,
ISI.

The timing landmarks on ECG (specifically the Q-time of the QRS complex) and on
the dZ/dt signal enable measurement of the Systolic Time Intervals, namely
the Ventricular Ejection Time, VET, and the Pre-Ejection Period, PEP.

The TEBCO®-measured parameters, i.e., the TFC, VET, EPCI, in conjunction
with the Volume of Electrically Participating Tissues, VEPT (a function of
patient's gender, height and weight), are used to calculate the Stroke Volume,
SV, according to Sramek's Equation:

SV = VEPT * VET * EPCI

Note 1: This equation reflects the physiologic basis of SV
determination: (a) SV is directly proportional to the physical size of a patient
(i.e., to VEPT - body habitus scaling constant), (b) SV is directly proportional
to duration of delivery of blood into the aorta (i.e., to VET), and (c) SV is directly
proportional to the peak aortic blood flow (i.e., to EPCI).Note 2: This
equation corrected most of the deficiencies associated with the original TEB Kubicek's
equation, used in the '70s.

The Systolic Time Intervals are then used to calculate an estimate ofEjection Fraction, EF, as

EF = 0.84 - 0.64(PEP / VET)

When SV is normalized by the Body Surface Area, BSA, the hemodynamically-significant
blood flow parameter called the Stroke Index, SI, is calculated as

SI = SV/BSA

BSA [m]
is a complex function of a patient's height and weight, calculated by TEBCO®
from the DuBois & DuBois formula:

The perfusion significant blood flow - the Cardiac Index, CI, is
then calculated as